The ancient Greeks and Romans knew of only five 'wandering stars' (Greek: πλανήται, planētai): Mercury, Venus, Mars, Jupiter, and Saturn. Following the discovery of a sixth planet in the 18th century, the name Uranus was chosen as the logical addition to the series: for Mars (Ares in Greek) was the son of Jupiter, Jupiter (Zeus in Greek) the son of Saturn, and Saturn (Cronus in Greek) the son of Uranus. What is anomalous is that, while the others take Roman names, Uranus is a name derived from Greek in contrast to the Roman Caelus.
So if you can name the planets in order, you're also able to quote Greek family history. Neat, huh?
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